Ruthenium is one of the most promising materials for capacitor electrodes for the next generation DRAM devices, as well as for barrier and/or seed layers between a copper layer and a Low-k dielectric layer. Now, high dielectric constant (high k) materials such as aluminum oxide (Al2O3) tantalum pentaoxide (Ta2O5) hafnium oxide and related materials, or Barium Strontium Titanate (BST) are used in capacitor cells and the process uses temperature up to 600° C. At such temperatures the oxidation of polysilicon, silicon, or aluminum occurs leading to capacitance loss. Ruthenium, as well as ruthenium oxide, have both high oxidation resistance and high electrical conductivity, and can be used as a capacitor electrode and an effective barrier against oxygen diffusion. Ruthenium is also used as a gate metal for lanthanide oxide. Besides, it is easily dry etched by ozone or by plasma techniques with oxygen, which is not the case of platinum and other noble metal compounds. Ruthenium may also be used as a barrier layer and a seed layer to separate a low-k material layer from an electrochemically deposited copper.
Many different precursors have been suggested to be used for ruthenium or ruthenium oxide layers deposition: Bis(ethylcyclopentadienyl)Ruthenium, [Ru(EtCp)2], pure or dissolved in a solvent (e.g. tetrahydrofurane), is frequently used as a precursor: It is liquid at room temperature, with a vapor pressure of 0.1 Torr at 75° C. Ru or RuO2 films are usually deposited using this precursor by CVD at temperatures between 300° C. to 400° C., and more recently by Atomic Layer Deposition (ALD), using oxygen as a reactant.
Ruthenocene (RuCp2) which has a melting point around 200° C., is also one of the precursors frequently used to deposit Ru or RuO2 in the same range of temperature as Ru(EtCp)2, with the same reactant, by CVD or ALD.
Tris(2,4-octanedionato)ruthenium [Ru(OD)3], which is liquid at room temperature and has a vapor pressure of 1 Torr at 200° C. is also used as a precursor by CVD deposition in a temperature range around 300° C.
US 2004/0241321 discloses “sandwiched” precursors, i.e., with the ruthenium atom centered around two of these Op ligands.
U.S. Pat. No. 6,605,735 discloses “half-sandwich” precursors with the ruthenium atom centered around one Op ligand and one cyclic-type (cyclopentadienyl for instance) ligand (The molecule, whatever the structure, has 18 electrons (8 from the Ru, 5×2 from the Op or Cp) and is thus stable.
There are several issues for the man skilled in the art when depositing a Ru or RuO2 layer or film on a substrate:                (a) the poor adhesion of such layer/film to the substrate;        (b) the presence of impurities in the film deposits on that substrate: the presence of impurities such as carbon in the deposited layer increases the resistivity of the film. Other impurities such as oxygen, hydrogen, and/or fluorine are sometimes present in the deposited layer, depending on the precursor composition.        (c) the delivery of the Ru precursor product may not be easy, due to the low vapor pressure of these precursors, which are sometimes solid, also raise concerns.        (d) the incubation time of Ru(EtCp)2: This incubation time may be reduced by using Ru(dmpd)(EtCp). A sputtering deposition seed layer before Ru deposition is sometimes necessary to avoid this incubation time at the initial stage of the growth when using Ru(EtCp)2         (e) some precursors have a very low volatility which decreases the deposition speed of the process.        
Ruthenium films are often deposited on oxygen sensitive surfaces made of nitrides, or pure metal, such as Ta or TaN. The use of oxygen as a co-reactant is therefore undesired as it results in the partial oxidation of the underlying layer.
According to the invention, these (and other) issues are solved by the use of ruthenium precursors for ruthenium containing film deposition selected from the group comprising: Ru(XOp)(XCp), Ru(XOp)2, Ru(allyl)3, RuX(allyl)2, RuX2(allyl)2, Ru(CO)x(amidinate)y, Ru(diketonate)2X2, Ru(diketonate)2(amidinate)2 their derivatives and any mixture thereof.
The precursor used may be a mix of open and cyclic ligands or direct bonds. The cyclic or more generally “closed” ligands are rings comprising between 2 and 12 carbon atoms. Preferably, the precursor used shall have double bonds which increase the stability of such precursor. However, the precursor may possibly have no carbon double bond if desired -diene, -triene, -tetraene, or similar bounds are used instead.
Preferably, ligands such as cyclopentadienyl, cyclohexadiene, cycloheptadienyl, norbornadiene, cyclooctadienyl, cyclooctatetraene may be used. Preferably, at least, one of the carbon atoms of these closed ligands preferably all of them may independently be bounded with molecules selected from the group comprising H, alkyl groups (C<16), perfluorocarbon groups (CXF(2X+1), C<16), amino compounds or any other group that may improve the characteristics of the molecules or of the resulting films.
To improve reactivity of the precursors according to the invention, it is preferred to select those precursors having one or several open-ligands (volatility will thereby increase). Allyl containing precursors are known for example to have a higher volatility than other organometallic compounds. The melting point of the various compounds exemplified hereinbelow is lower than 150° C., in order to ease the delivery up to the deposition chamber. Preferably, the melting point of a precursor according to the invention shall be at most equal to 100° C. and more preferably, at most equal to 50° C. or even below room temperature to allow its delivery as a liquid.
The high reactivity of such precursors enables low temperature deposition and less film impurities. The high volatility of the precursors according to the invention also provide high deposition rates and allows no heating of the delivery lines of the precursors. The stability of these precursors comprising molecules with an outer shell which is electronically filled is also improved. Finally the precursors according to the invention reacts with hydrogen and not oxygen (as those of the prior art), which will prevent them from generating oxygen-containing interface layer between the ruthenium film and the substrate.